[Mr70]

I believe air cleaners were the final dressing,so they wouldn't be sitting on engines early on.
Added on after the carburetor,which was not put on until after the engine was assigned to a body sequence number.
Aside from the Camaro,not every CKO engine received them.
And TH400 vehicles also recieved the Dual,stamped CTY for Novas and CRR for LS-6 Chevelles.